Synergistic promotion of dielectric and thermomechanical properties of porous Si₃N₄ ceramics by a dual-solvent template method

Porous Si₃N₄ ceramic is a promising high-temperature wave transparent material used as a radome or antenna window of hypersonic aircraft. However, it still faces a challenging trade-off between dielectric and thermomechanical properties. Therefore, tailoring the microstructure and properties of porous Si₃N₄ is of great significance. In this work, porous Si₃N₄ ceramics with uniform and fine structures were achieved by the dual-solvent templating combined freeze-casting method. The as-prepared porous Si₃N₄ ceramic, with 56% porosity, possesses high mechanical properties with flexural strength and compressive strength of 95±14.8 MPa and 132±4.5 MPa, respectively. The uniform spherical pore structure improves the mechanical properties, and the rod-shaped Si₃N₄ grains facilitate crack deflection. The decreased pore size effectively blocks the phonon transport leading to a low thermal conductivity of only 4.2 W·K^-1·m^-1. Meanwhile, the porous Si₃N₄ ceramic maintains a small dielectric constant of 3.3 and the dielectric loss is stable between 1.0×10^-3~4.0×10^-3, which guarantees its potential application in high-temperature wave-transparent components. The results contribute a significant advancement in the development of high-performance wave-transparent materials used in hypersonic aircraft.